Not getting correct aspect ratios when exporting game

Total noob here. I am trying to export my game and I think I am enforcing a 16:9 aspect ratio by going to build settings -> player settings -> support aspect ratio's and then deselecting everything except 16:9. However when I open up the game, it cuts off the sides and looks like it's a 2:3 ratio or something. Anyone know where I have gone wrong?